Genetic diversity of the Italian thoroughbred horse population

For over three centuries, thoroughbred (TB) horses have been selected exclusively for traits enhancing racing performances. Officially the TB origins can be genetically traced back along the male line due to the crossbreeding among 50 English royal mares and four Arab oriental stallions in 1700s. Because of the TB population is tightly controlled, possible loss of genetic variability should be carefully evaluated for breed conservation and management programme. To this aim FTA (R) cards of 10032 TB foals over a 14-year new-born campaign period were collected for genetic variability evaluation using 16 microsatellite markers. Total number of allele was 118 with a mean value of 7.37 alleles per locus; Polymorphic information content (PIC) values were above the informative threshold (PIC >0.5) for all microsatellites except for HTG4 and HMS2 whereas no significant differences were showed between the mean expected (H-e) and observed heterozygosity (H-o) values (0.674 vs. 0.675, respectively). Hardy-Weinberg proportion exhibited no statistically significant deviation from equilibrium (p < .05) for all loci; the inbreeding coefficient mean was close to zero suggesting very low probability of autozygosity. The number of genotypes observed (N-g) was calculated for each microsatellite and the most representative was found at the HMS2 locus (LL, frequency 0.557). Parentage testing was also investigated reporting a combined probability of identity (PI) for the 16 loci of 4.1 x 10(-14) while the probability of exclusion (PE) exceeded 99% in all cases. Overall data reported a reasonable level of informativeness which genuinely reflect the narrower genetic structure of the Thoroughbred population. HIGHLIGHTS Thoroughbred population from Italy did not show any significant evidence for close inbreeding; a moderate level of genetic diversity was found at some loci yet still adequate for parentage and identity verification. Appropriate management programme could be placed to introduce new genetic variability in the Italian Thoroughbred population.